1. Field of the Invention
The present invention relates to an image forming apparatus capable of producing an enlarged (scale-up) copy of an original image by dividing the original into a number of areas depending on the magnification (scale factor) of copy and producing an enlarged cop of each divided area on a sheet of copy paper sequentially so that a copied image larger than the size of copy paper is obtained.
2. Description of the Related Art
Copy machines based on digital image processing have a function in which an original is divided into a number of areas depending on the magnification of copy and an enlarged copy of each divided area is produced on a sheet of copy paper sequentially so that a copied image larger than copy paper is produced. This copy process will be called "conjunct scale-up copy" hereinafter.
In the conjunct scale-up copy operation, an original image is partially copied by being enlarged onto a sheet of paper at a time, and sheets of copied paper are delivered sequentially. The operator lays out the sheets of copied paper properly to get an enlarged copy of the original in the form of a set of partial images.
Conventional copy machines with the conjunct scale-up copy function are designed to use one sheet of copy paper for each divided area of the original. For example, when an A3-sized original is copied with the magnification of 5.0 onto sheets of A3-sized paper, the original is divided by five horizontally and vertically into 25 areas, and 25 divided original images are copied onto 25 sheets of paper, i.e., copy paper equal in number to the divided areas is used.
Accordingly, when the original size and copy paper size are equal and the magnification is an integer (greater than one), the size of an enlarged copy is equal to the total size of sheets of paper used to make an enlarged copy. The number of sheets of paper is equal to the square of the magnification. However, if the original size and paper size are different even though the magnification is an integer, or if the magnification is a fractional number, part of at least one sheet of paper is left unused and therefore copy paper is often wasted.
For example, for making a copy with the magnification of 1.5 of an original image Gi on an original D by using copy paper of the original size, four sheets of paper P are needed as shown in FIG. 55 . In this case, although one sheet of paper is fully used to form a partial image Gh1, other two sheets of paper have their 50% area left unused and another sheet of paper has its 75% area left unused.
In making a copy with the magnification of 4.0 of an image Gi of an original D by using copy paper P of the original size as shown in FIG. 56 (a), the original D is divided by four horizontally and vertically into 16 areas e1-e16, as shown in FIG. 56 (b). These areas e1-e16 are copied from the leftmost area to the rightmost area on a row and from the top row row to the bottom row sequentially, i.e., in the order of e1.fwdarw.e2.fwdarw.e3.fwdarw.e4.fwdarw.e5.fwdarw.e6.fwdarw.e7.fwdarw.e8.f wdarw.e9.fwdarw.e10.fwdarw.e11.fwdarw.e12.fwdarw.e13.fwdarw.e14.fwdarw.e15. fwdarw.e16. As a result of the iterative copy operations, 16 sheets of copied paper P starting with the one having a formation of a partial copied image Gh1 and ending with the one having a formation of a partial copied image Gh16 are delivered sequentially as shown in FIG. 56(c).
The conjunct scale up copy operation takes a relatively long time to complete the entire original area when the number of divisions, which is determined from the magnification and paper size, increases.
On the other hand, at the operator's assessment of a copy work, attention is often paid to a specific portion of the original depending on the purpose. An example of such portion is the human skin where delicate hue adjustment is required in copying a color portrait. In the example of FIG. 56(b), when the operator pays attention to the original in the area ell, the operator may have to retry the conjunct scale-up copy operation by altering the conditions such as the magnification and hue adjustment if the copied partial image Gh11 for the area e11 is found unsatisfactory. In this case, the conventional copy machines do not allow the operator to examine the quality of the copied image Gh11, which is delivered by the 11th copy operation, at an early stage of operation.
In addition to the above-mentioned problem of operation ability, even if the operator makes a decision of retry at the delivery of the copy for the area ell, ten sheets of paper and time expended for them are wasted.
A further problem of the conventional copy machines is that during the conjunct scale-up copy operation, if all copy paper stacked in the supply cassette runs out, the copy operation is shut off abruptly. In this case, it is necessary for the operator to supply copy paper and start the copy operation from the beginning, resulting in the waste of paper and time expended before the machine was shut off.